Gil Evans spent his earliest years traveling around Canada with his family, as they were regularly forced to move in order to follow the availability of mining jobs for his stepfather. In 1922 the family settled in Berkeley, and it was shortly afterward that Gil first developed an interest in music, inspired by a Duke Ellington concert he had been brought to by a family friend. His training began with piano lessons, but he largely taught himself through listening to and transcribing from his record collection. While in high school he took jobs in hotels as a pianist, and after graduation he formed an ensemble that would serve as the house band for the Rendezvous Ballroom in Balboa Beach for two years; in 1937 the band relocated to Hollywood, where it provided music for Bob Hope's radio broadcasts. Through his work for Hope, Evans was hired as an arranger for Claude Thorhill's orchestra, whom he continued to work alongside until 1948 - although with an interruption of several years when World War II prompted Evans to enlist in the army.

After his discharge from the military in 1946 Evans settled in New York. His efforts with Thornhill had gained him a solid reputation in the jazz community, leading to his involvement in the Miles Davis nonet in 1948; with this group he recorded the landmark album The Birth of Cool between 1949 and 1950, the album being finally released in 1953. During the first half of the 1950s Evans remained largely inactive, focusing his attention on musical study while occasionally arranging for television and radio, and for singers such as Tony Bennett and Johnny Mathis. He resumed his collaboration with Miles Davis in 1956, contributing to the following year's Miles Ahead and continuing with several more notable recordings up through the early 1960s. His first recordings under his own name were also made during this period, which would see him established as one of the leading names in the jazz world.

In 1964 Evans had his first of two children with his second wife, and for the majority of the remainder of the 1960s he devoted himself to raising his family. When he became active again in 1969, his work reflected the emerging music of the time, integrating electric instruments into the jazz-ensemble framework. A strong interest in the music of Jimi Hendrix developed during this time, and a record of jazz arrangements of his songs would be released in 1974 after Hendrix's death brought an end to plans for an actual collaboration between the two. Regular touring of the States and Europe continued throughout the 70s and 80s, with most of his recorded output being culled from these performances; several ventures into film scoring were also made in the 1980s, including contributions to Absolute Beginners and The Color of Money. A residency at the New York club Sweet Basil was established in 1984, which continued until Evans' death in 1988.